Donald Trump released his first television attack ad Friday as he and his chief Republican rival, Sen. Ted Cruz of Texas, moved into direct and more hostile contention.

With the Iowa presidential caucuses just 10 days away, the New York billionaire’s ad accuses Cruz of being “pro-amnesty” on illegal immigration. It shows Cruz tripping over his words as he tries to explain to Fox News why he proposed a Senate measure that would have granted legal status to millions of immigrants in the country illegally.

Trump then says immigrants are “pouring in” and “doing tremendous damage if you look at the crime, if you look at the economy.”

The attack underscored that Cruz’s popularity among evangelicals and tea party followers is the biggest obstacle standing in Trump’s way in Iowa — at least for now. Trump’s increasingly aggressive attacks on Cruz, along with his enlistment of Sarah Palin as his No. 1 surrogate, are part of his all-out push to firm up support among the state’s most conservative voters.

Cruz attacked Trump in an ad of his own on Friday. It portrays the real estate tycoon as a “fat cat developer” who colluded with Atlantic City, N.J., insiders “to bulldoze the home of an elderly widow” for a limousine parking lot at a Trump casino.

The ad shows the widow saying, “He doesn’t have no heart, that man.”

Cruz’s spot challenges Trump’s portrayal of himself as a people’s advocate who is paying for his own campaign and thus immune to sordid political deal-making that favors insiders over the public. By Cruz’s telling, insider deals underpin Trump’s sprawling business empire.

On Twitter, Trump defended the property condemnation by eminent domain.

“Ted Cruz complains about my views on eminent domain, but without it we wouldn’t have roads, highways, airports, schools or even pipelines,” he wrote.

Cruz is also under fire from another Republican opponent, Sen. Marco Rubio of Florida. Trump’s immigration ad amplifies a line of attack that Rubio has taken against Cruz for weeks.

Trump’s immigration ad was “factually false,” said Cruz spokesman Rick Tyler. “Ted Cruz led the fight against amnesty,” he said.

Tyler also said that Trump had supported amnesty in the past. He pointed to an August 2013 tweet from Trump: “Congress must protect our borders first. Amnesty should be done only if the border is secure and illegal immigration has stopped.”

Cruz’s sprawling on-the-ground operation in Iowa is widely seen as stronger than Trump’s, and the attacks could further threaten the senator’s position; an Iowa victory is crucial to his overall campaign strategy.

So far, Trump has proved immune to criticism from Jeb Bush and other rivals. But until now, most of his opponents had steered away from direct attacks on him. He has maintained a wide lead in national polls of Republicans.

In Iowa, where he has been virtually tied with Cruz, some polls suggest Trump has pulled slightly ahead in recent days, although others show Cruz leading.

In addition to the attacks from Cruz, Trump also came under fire Friday from an influential conservative magazine, the National Review, which devoted its weekly issue to a series of essays from conservative intellectuals denouncing the billionaire New Yorker as a phony conservative and a charlatan.

Palin’s endorsement of Trump this week could draw some of Cruz’s support among evangelical and tea party voters.

But when she used a Trump rally in Tulsa, Okla., on Wednesday to blame President Obama for the domestic violence arrest of her son Track, an Army veteran, it was a reminder of the controversy Palin has long attracted.

Trump told CNN it was his idea that she bring up the arrest, saying the troubles that Palin’s son suffered upon returning from Iraq were a good way to strengthen his case against the Obama administration’s veterans policies.

“Look at the horrible care our vets get,” Trump said. “One of the many things I’m going to do is straighten that mess out.”

Trump has dodged the question of whether he might name Palin as his running mate should he win the nomination, saying he didn’t think she wanted to reprise her 2008 role as a vice presidential nominee. But he said he was open to having her serve in his administration.

Her endorsement Tuesday at a rally in Iowa came as Trump tried to shore up support with the party’s most conservative voters. In an interview Thursday with Field & Stream, a magazine for hunters and anglers, Trump mentioned his membership in the National Rifle Assn.

“I do have a gun, and I have a conceal-carry permit, actually, which is a very hard thing to get in New York,” Trump said, adding: “My sons are major hunters.”

On Friday, Trump released a radio ad featuring Jerry Falwell Jr., the president of Liberty University, a Christian school in Virginia. The son of Moral Majority founder Jerry Falwell, a major leader of the religious right in the 1980s, he drew parallels between his father and Trump when he introduced the New York builder to an audience at the school on Monday.

“Like Mr. Trump, Dad would speak his mind,” Falwell said in remarks that Trump used in his ad. “He would make statements that were politically incorrect. He speaks the truth publicly, even if it is uncomfortable for people to hear it.”